In recent years, there has been proposed by 3GPP (3rd Generation Partnership Projects) and specified in non-patent document 1 a mobile wireless communication system called a W-CDMA (Wideband-Code Division Multiple Access) system or a UMTS system (Universal Mobile Telecommunications System), which is based on Code Division Multiple Access (CDMA).
FIG. 1 illustrates an example of a typical configuration of a W-CDMA system. This system is composed of mobile stations (User Equipment: UE) 11, 12 having a wireless communication function, wireless base stations (Node B) 21, 22 having a function of wireless communication with the mobile stations, radio network controllers (RNC) 31, 32 that are connected to corresponding wireless base stations and perform a wireless control operation, and an exchange station 60 that is connected to the radio network controllers and performs an exchange operation. This configuration enables communications between the mobile station 11 and the mobile station 12.
Here, a network including the wireless base stations 21, 22 and the radio network controllers 31, 32 is called a radio access network (RAN) and a network including the exchange station is called a core network (CN). Although a core network 80 can generally include a plurality of layered exchange stations and also other apparatuses such as a home memory storing subscriber information, FIG. 1 shows only one exchange station 60 and omits other apparatuses in order to simplify the explanation.
In the system shown in FIG. 1, user data can be transmitted from the mobile station 11 to the mobile station 12. In this case, the user data travel through a transfer path of the mobile station 11, the wireless base station 21, the radio network controller 31, the exchange station 60, the radio network controller 32, the wireless base station 22, and the mobile station 12 in this order. For descriptive purposes, communication through such a path is referred to as an external communication hereinafter.
FIG. 2 illustrates a shortcut communication path that routes through not the exchange station but a transmission apparatus. Radio access networks 71, 72 shown in FIG. 2 are provided with transmission apparatuses 41, 42, respectively. The user data travel through a transfer path of the mobile station 11, the wireless base station 21, the transmission apparatus 41, the transmission apparatus 42, the wireless base station 22, and the mobile station 12 in this order. For descriptive purposes, communication through such a transfer path is referred to as an internal communication. Such a transmission path serves as a transmission function that reduces workload on various lines and a core network apparatus such as the exchange station 60, and is more frequently adopted in an Internet-Protocol (IP)-based radio access network, reported in non-patent document 2 below. This is because the IP is a connectionless protocol and allows for data transfer based only on a calling and a receiving address without attention to a path therebetween for the internal communication.
FIG. 3 shows an example of a protocol stack in the W-CDMA system. In this figure, wireless physical layers 311, 321 terminate respectively in the mobile station 11 and the wireless base station 21, having a function of wireless communication. Wireless data link layers 313, 336 terminate respectively in the mobile station 11 and the radio network controller 31, having a function of data link control over a wireless communication path, such as re-transmission control, data confidentiality, integrity protection or the like.
Here, data transmitted and received between the wireless data link layer 336 and the wireless physical layer 321 are transported in the radio access network by a protocol called Iub UP defined over the transport path of a transport protocol such as UDP/IP protocol. This transport path is called a “transport bearer” 351. In addition, data transmitted and received between the radio network controller 31 and the core network are transported through a transport path called an “Iu bearer” 380 configured by an Iu transport protocol. Here, since the Iu transport protocol is not directly related to the present invention, detailed explanation thereof is omitted. A user layer 390 is defined as an upper layer over the wireless data link layers 313, 336 and the Iu transport protocols 331, 361. The user data are transparently transferred through a radio access system by a “radio access bearer” 371 configured between the mobile station 11 and an intended party by a group of the protocols as explained above.
FIG. 4 illustrates an example of a protocol stack in the internal communication in the W-CDMA system. In the internal communication, a wireless data link layer 346 and a transport bearer 352 are terminated by not the radio network controller but the transmission apparatus 41. Data transmission/reception is carried out between the transmission apparatus 41 and the transmission apparatus 42. Except for this, the same explanation given with reference to FIG. 3 is applied.
The system shown in FIG. 4 supports both the external and the internal communication and includes a function of selecting either the external communication or the internal communication at every event of communication, and a function of switching between the external communication and the internal communication during communications. The latter function is to allow for switching to the internal communication after a caller is off-hook, by transmitting a ring-back tone through the external communication at the time of calling, or to allow for an answer to a call taking place over the external (internal) communication during communications over the internal (external) communication.
Next, there will be outlined a conventional method that has since been contemplated for switching to-and-fro between the external communication and the internal communication. In the communications based on the protocol stack shown in FIGS. 3 and 4, the conventional method for switching from the external communication to the internal communication requires re-establishment of a radio access bearer. Namely, while a new radio access bearer 372 is established, the radio access bearer 371 used for the external communication is released. This means that there has to be carried out resetting of the wireless physical layers 311, 321 and the wireless data link layers 313, 336; re-establishment of the transport bearer 351; and elimination of the Iu bearer 380.
FIG. 5 is an example of a sequence contemplated in the past that shows procedures of switching from the external communication to the internal communication. When detecting a trigger for switching to the internal communication during the external communication, the radio network controller 31 instructs the wireless base station 21 to establish a new wireless physical layer for the internal communication. Upon being instructed, the wireless base station 21 establishes a wireless physical layer based on the instruction and then starts to transmit radiowaves. Subsequently, the radio network controller 31 instructs the transmission apparatus 41 to establish a new wireless data link layer and a transport bearer for the internal communication. Upon completion of the instruction, the radio network controller 31 instructs the mobile station 11 to re-establish a wireless physical layer and a wireless data link layer. At this time, the mobile station 11 is notified of establishment information on the wireless physical layer and the wireless data link layer that have been established in the wireless base station 21 and the transmission apparatus 41, respectively.
Upon being notified, the mobile station 11 performs re-establishment of a wireless physical layer and wireless data link layer from the old wireless physical layer and wireless data link layer for the external communication to a new wireless physical layer and wireless data link layer for the internal communication. Namely, the mobile station 11 performs a transition to a new radio access bearer. Here, re-establishment of a wireless physical layer means re-establishment of a wireless physical connection identified by a diffusion code in the W-CDMA system. In addition, re-establishment of a wireless data link layer means initialization of an order control sequence number and a parameter relating to re-transmission. Next, the radio network controller 31 releases the wireless physical layer for the external communication, the Iu bearer 380 between the radio network controller and the exchange apparatus, the wireless data link layer 313 and the transport bearer 351, which have all become unnecessary now, thereby completing the sequence. By the way, switching from the external communication to the internal communication has been explained above; opposite switching from the internal communication to the external communication can be explained based on the same idea. Moreover, while switching between the radio network control 31 and the transmission apparatus 41 has been explained above, switching between the two transmission apparatuses can generally be realized in the same procedures.    Non-patent document 1: 3 GPP Technical Specifications TS21.101    Non-patent document 2: 3 GPP Technical Reports TR25.933